1. Field
One embodiment of the present invention relates to an inspection device and inspecting method for a spatial light modulator, an illumination optical system, a method for adjusting the illumination optical system, an exposure apparatus, and a device manufacturing method. For example, the embodiment of the present invention relates to inspection of a spatial light modulator suitably applicable to an illumination optical system of an exposure apparatus for manufacturing devices such as semiconductor devices, imaging devices, liquid crystal display devices, and thin film magnetic heads by lithography.
2. Description of the Related Art
In a typical exposure apparatus of this type, a light beam emitted from a light source travels through a fly's eye lens as an optical integrator to form a secondary light source (a predetermined light intensity distribution on an illumination pupil in general) as a substantial surface illuminant consisting of a large number of light sources. The light intensity distribution on the illumination pupil will be referred to hereinafter as a “pupil intensity distribution.” The illumination pupil is defined as a position such that an illumination target surface becomes a Fourier transform plane of the illumination pupil by action of an optical system between the illumination pupil and the illumination target surface (a mask or a wafer in the case of the exposure apparatus).
Beams from the secondary light source are condensed by a condenser lens to superposedly illuminate the mask on which a predetermined pattern is formed. Light passing through the mask travels through a projection optical system to be focused on the wafer, whereby the mask pattern is projected (or transferred) onto the wafer to effect exposure thereof. Since the pattern formed on the mask is a highly integrated one, an even illuminance distribution must be obtained on the wafer in order to accurately transfer this microscopic pattern onto the wafer.
There is a hitherto proposed illumination optical system capable of continuously changing the pupil intensity distribution (and, in turn, an illumination condition) without use of a zoom optical system (See Japanese Patent Application Laid-open No. 2002-353105). In the illumination optical system disclosed in Japanese Patent Application Laid-open No. 2002-353105, using a movable multi-mirror composed of a large number of microscopic mirror elements which are arranged in an array form and an inclination angle and inclination direction of each of which are individually driven and controlled, an incident beam is divided in microscopic units by respective reflecting surfaces to be deflected thereby, so as to convert a cross section of the incident beam into a desired shape or desired size and, in turn, so as to realize a desired pupil intensity distribution.
Since the illumination optical system described in Japanese Patent Application Laid-open No. 2002-353105 uses the reflection type spatial light modulator having the large number of microscopic mirror elements whose postures are individually controlled, degrees of freedom are high about change in shape and size of the pupil intensity distribution. However, there is a possibility that, for example, reflectances of reflecting surfaces of the mirror elements made of aluminum will decrease with time because of irradiation with light and it will become difficult to form a desired pupil intensity distribution because of influence of the reflectance decrease.
An embodiment of the present invention has been accomplished in view of the above problem and it is an object of the present invention to provide an inspection device and inspecting method capable of inspecting the reflectances of the mirror elements of the spatial light modulator arranged in the optical path of the illumination optical system, for example, on an as-needed basis. It is another object of the present invention to provide an illumination optical system capable of achieving a desired pupil intensity distribution, using the inspection device for inspecting the reflectances of the mirror elements of the spatial light modulator arranged in the optical path, for example. It is still another object of the present invention to provide an exposure apparatus capable of performing excellent exposure under an appropriate illumination condition, using the illumination optical system achieving the desired pupil intensity distribution.